The invention relates to a front hood system of a motor vehicle.
When motor vehicles collide with pedestrians, the front portion of the motor vehicle forms an impact surface which has to be provided with a defined flexibility in order to avoid or at least to reduce injuries to individuals. The central region of the front hood, which is of planar design, may be designed such that it is correspondingly elastically or plastically deformable.
In the driving mode, in which the front hood is closed, the latter rests on corresponding supporting points of the surrounding body parts, such as the wing, front subassembly or the like. In the region of the supporting points mentioned, there is only slight vertical flexibility. For example, in the event of a vertical head impact in this region, the lack of flexibility may give rise to undesirably high impact accelerations. In addition, in the case of vehicles with a front engine, increasingly stringent demands regarding the absorption of noise require effective countermeasures in the region of the front hood. In addition to a planar lining of the engine hood with a suitable sound-absorbing mat, a means of absorbing noise may also be required in the region of the encircling front hood edge.
Front hood systems are known, in which the body-side supporting points for the front hood are designed flexibly in the vertical direction to reduce the consequences of an impact. For adequate flexibility, a corresponding construction height is required which is not always provided in the constricted parts of a front portion of a motor vehicle. Measures for absorbing noise and for sealing the front hood in the region of its edge may adversely affect the desired flexibility in this region.
The invention is based on the object of developing a front hood system in such a manner that the front hood, in the region of its edge, has improved impact flexibility without having an adverse effect on the sealing of the edge.
For this purpose, in order to form the flexible, body-side supporting points, a linearly encircling supporting strip with a sealing strip situated between the supporting strip and the front hood is provided. In this case, the front hood has, on its side facing the supporting strip, an absorption strip which encircles it in a manner corresponding to the body-side supporting strip and can be brought to bear against the sealing strip. When the front hood is closed, the absorption strip, the sealing strip and the supporting strip are pressed onto one another, with the closing forces or counterforces occurring leading in conjunction with the associated, elastic deformation to a reliable, encircling sealing-off of the engine hood from the body parts situated around it. At the same time, the absorption strip and supporting strip, which is flexible in the vertical direction, form a joint potential for deformation with an overall high deformation distance. If the abovementioned parts are appropriately mechanically configured, a large amount of impact energy can be absorbed over an overall large deformation distance, as a result of which impact accelerations which occur are kept to a correspondingly low level. In customary operation, the encircling sealing strip on the flexible supporting strip provides reliable sealing and contributes to the absorption of noise without restricting the deformation distance, which can be achieved structurally, of the absorption strip and supporting strip.
In one embodiment, the front hood has, at least over a partial region of its outer edge, an outer region reaching from the absorption strip as far as the outer edge, a clearance extending over the width of the outer region in the vertical direction as far as the supporting strip situated below. This design avoids, in the event of a vertical impact, the designated deformation distance being limited by the hood outer edge striking against a body part situated below it. An overall deformation distance is available which is composed of the individual deformation distances of the absorption strip and of the flexible supporting strip.
In another embodiment, the supporting strip has a doubly bent, approximately Z-shaped cross section with a free limb for receiving the sealing strip and a retaining limb secured on the adjacent body part. In this case, the free limb lies in the vertical direction below the retaining limb. The effect achieved by this arrangement is that, in the closed state of the hood, the cross section of the absorption strip lies approximately laterally next to the central part of the Z-shaped cross section of the supporting strip. An overall small construction height of the flexible system comprising the absorption strip, the sealing strip and the supporting strip is produced.
In this case, the supporting strip is advantageously manufactured from plastic. Given a suitable structural design, an elastoplastic behavior of the supporting strip in terms of flexibility that reduces the impact accelerations can readily be obtained.
To improve the sound-absorbing effect, the absorption strip is advantageously coated with a sound-absorbing material on its side facing the sealing strip. For this purpose, the sound-absorbing material is in particular formed by a sound-absorbing mat which is fitted on the inside of the front hood and is drawn around the absorption strip. In the closed state of the hood, the sound-absorbing material bears, in a planar manner, against the sealing strip. The overall elastically flexible supporting system of the front hood leads to a uniform, planar bearing with correspondingly good sound-absorbing effect without the desired elastoplastic behavior in terms of flexibility in the event of an impact being impaired.
To produce a defined contact pressure with good plastic energy absorption behavior, the absorption strip expediently has an approximately trapezoidal cross section, the narrow side of which can be brought to bear against the sealing strip.
The absorption strip is advantageously formed from a rigid synthetic foam. In the event of an impact load, the foam bubbles of the rigid foam collapse in the manner of a cascade, as a consequence of which a high energy absorption with comparatively low force peaks is provided over the entire deformation distance. In an advantageous alternative, the absorption strip is formed from a plastic hollow trough. The plastic hollow trough can be produced with little outlay in terms of manufacturing and is easy to fit. From the onset of a certain limit force, the cross section collapses and results in a desired energy-absorbing flexibility. Below the limit load, the hollow cross section of the plastic hollow trough has an elastic flexibility. Height tolerances in the encircling sealing system can be correspondingly readily compensated for. Smaller additional loads can readily be absorbed without the absorption strip being damaged.